Image signal recording and reproducing apparatus

ABSTRACT

A first digital processor (13) generates luminance data Y and color difference data U, V, using image data D1. The processor (13) further generates separated luminance data Y1, Y2 by halving the luminance data Y, and generates a compound color difference data C by combining the color difference data U, V for output. An JPEG encoder 13 compresses the separated luminance data Y1, Y2 and the compound color difference data C to generate compressed luminance data y1, y2 and compressed color difference data c. A modulator 15 modulates the compressed luminance data y1, y2 and the compressed color difference data c to generate luminance modulated signals m1, m2 and color difference modulated signal mc. A recording/reproducing section 16 records the luminance modulated signals m1, m2 and the color difference modulated signal mc in parallel onto the first to third recording tracks of a magnetic tape (20).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image signal recording andreproducing apparatus which compresses an image signal for color displayand records the compressed image signal in magnetic recording media. Thepresent invention further relates to an image signal recording andreproducing apparatus which can easily record an image signal for colordisplay.

2. Description of the Related Art

In an imaging device, such as a TV camera using a CCD image sensor,horizontal and vertical scanning timings are determined based on varioussynchronizing signals according to a predetermined television format. Asa result of scanning an object at determined timings, image informationfor one image picture, or one scene, is gathered, and transformed inorder to be conveyed by successive image signals arranged in apredetermined order.

FIG. 19 is a block diagram representing a basic structure of an imagingdevice using a CCD image sensor; FIG. 20 is a diagram indicatingoperation timings of the device of FIG. 19.

A CCD image sensor 1 of a frame transferring type comprises an imagingdevice 1i, a storage 1s, a horizontal slider 1h, and an output section1d. An imaging device 1i consists of a plurality of CCD shift registerswhich are arranged parallel to each other and successive in the verticaldirection. Each bit of the respective shift registers constitutes alight receiving pixel element for storing information charges generatedwhile taking images.

Storage 1s, comprising a plurality of CCD shift registers having as manybits as those of the sensor 1, is continuous with the shift registers ofthe imaging device 1i. Each bit of the respective shift registerstemporarily stores the image charges supplied from each light receivingpixel element of the imaging device 1i.

The horizontal slider 1h, comprising a single CCD shift register eachbit of which is coupled to an output of each shift register of thestorage 1s, sequentially shifts the information charges supplied forevery horizontal line from the storage 1s, toward the output section 1d.

The output section 1d is located on the output side of the horizontalslider 1h, and has a capacity for receiving information charges slidtoward the output section 1d. The section 1d generates a voltage whosevalue varies depending on the amount of supplied information charges.The variation serves as an image signal 10.

A driver circuit 2 comprises a frame clock generator 2f, a verticalclock generator 2v, a horizontal clock generator 2h, and a reset clockgenerator 2r. The frame clock generator 2f generates a frame clock φf inresponse to a frame shift timing signal FT, and supplies the clock φf tothe imaging device 1i so that information charges stored in therespective light receiving pixel element of the imaging device 1i aretransferred to the storage 1s at high speed each vertical scanningperiod.

The vertical clock generator 2c generates a vertical clock φv inresponse to a vertical synchronizing signal VT and a horizontalsynchronizing signal HT, and supplies the signal φv to the storage ls sothat the storage 1s tentatively stores the image charges supplied fromthe imaging device 1i, and forwards the charges further to thehorizontal slider 1h for every horizontal scanning line in everyhorizontal scanning period.

The horizontal clock generator 2h generates a horizontal transfer clockφh in response to a horizontal synchronizing signal HT, and supplies thesignal φh to the horizontal slider 1h so that the slider 1h sequentiallyslides the information charges supplied from the storage 1s for everyhorizontal line toward the output section 1d.

A reset clock generator 2r generates a reset clock φr, and supplies theclock φr to the output section 1d so that the information charges slidby the horizontal slider 1h toward the output section 1d for everypixel, are stored in the output section 1d and then outputted insynchronism with the operation of the horizontal clock generator 2h.

A timing control circuit 3, which operates based on a reference clockhaving a constant cycle, generates a vertical synchronizing signal VTand a horizontal synchronizing signal HT for determining the timings atwhich the image sensor 1 executes vertical and horizontal scanning, andsupplies the signals to the driver 2. The circuit 3 also generates aframe shift timing signal FT having the same cycle as that of a verticalsynchronizing signal VT, and supplies the signal FT to the drivercircuit 2. The timing control circuit 3 is responsible for a shuttercontrol so as to keep the image sensor 1 in the optimum exposure state.Specifically, the circuit 3 instructs the imaging device 1i to output,during a vertical scanning operation, information charges storedtherein, according to the amount of information charges caused andstored thus far in the imaging device 1i. That is, when the circuit 3sets a faster shutter operation timing for outputting informationcharges from the imaging device 1i, information charges stay in theimaging device 1r in a longer period of time. On the other hand, whenthe circuit 3 sets a slower shutter timing, information charges stay inthe imaging device 1r in a shorter period of time before an image takingoperation is conducted with respect to the next picture frame beforelong. Note that a shutter operation is executed according to a driverclock supplied to the image sensor 1 by the driver circuit 2 to theimage sensor 1.

An image signal I0 obtained through the above processes is supplied to aconventional television monitor or a recording device to be used forrepeatedly displaying object images in the unit of an image picture at aframe rate determined corresponding to a vertical synchronizing signalVT.

It has also been attempted to input an image signal obtained by animaging device into a personal computer or the like, as digital imagingdevice, to be used for displaying an image on the monitor screenthereof. An image obtained by an imaging device is seldom displayed on afull screen. Rather, it is generally compressed to be display a smallimage on the screen. As an image format adaptable to such a displayingmanner, Common Intermediate Format (CIF) (352×240 pixels) and QuarterCIF (QCIF) standards (176×120 pixels) are available. CIF defines a sizeabout a quarter of that of the Video Graphic Array (VGA) standard(640×480 pixels), which is one of the major personal computer monitorstandards; QCIF define a size about a quarter that of the CIF standards.These standards are becoming widely accepted.

In an imaging device employing CIF or QCIF, the number of pixelsaccording to the respective standards are installed into the imagesensor. With these devices, the cost of an imaging unit is smaller thanfor conventional imaging devices adopted to general television formats,such as NTSC or PAL.

However, a recording format dedicated to imaging devices, such as theVHS format available for NTSC, has yet to be proposed for CIF or QCIF.Therefore, it has long been desired to determine a format in which imagesignals are recorded so as to be adopted to the above devices.

Conventionally, a digitally converted image signal is inputted into acomputer device in a predetermined format, and stored in a recordingmeans incorporated into or connected to the computer device. However,the imaging device must remain continuously connected to the computer inthis method in order to introduce an image signal from the device to acomputer. This is quite inconvenient.

SUMMARY OF THE INVENTION

The present invention has been conceived to overcome the above problemsand aims to provide an image recording and reproducing apparatus capableof easy recording of image signals for displaying a smaller imagepicture consisting of a fewer number of pixels, using a magnetic tape.

In a first aspect of the present invention, there is provided (claim 1).

In this aspect, two types of luminance modulated signals stemming on aluminance signal, and one color difference modulated signal made bycombining two types of color difference signals, are recorded inparallel in the first to third recording tracks of a recording medium. Aluminance signal having a large information amount is halved so as toeach have a lower frequency. Color difference signals each having asmall information amount are combined together to be recorded in onerecording track.

With this arrangement, it is possible to record an image signal forcolor images in an audio cassette tape which generally has fourrecording tracks.

According to a second aspect of the invention, there is provided (claim3).

In this aspect, two types of luminance modulated signals read from arecording medium is combined into one luminance signal, while a colordifference modulated signal is halved into two types of color differencesignals.

According to a third aspect of the invention, there is provided (claim5).

In this aspect, two types of luminance modulated signals stemming on aluminance signal, and one color difference modulated signal made bycombining two types of color difference signals, are recorded inparallel, together with an audio signal including a timing clock signal,in the first to fourth recording tracks of a recording medium. Aluminance signal having a large of amount information is halved, so asto each have a lower frequency. Color difference signals each having asmall information amount are combined together to be recorded on onerecording track. Also, an audio signal including fewer high frequencycomponents is superimposed by a timing clock signal in a high frequencyband matching the modulation cycle of the luminance modulated signalsand the color difference modulated signal, to be recorded in onerecording track.

With this arrangement, it is possible to record an image signal forcolor image on an audio cassette tape with four recording tracks. At thesame time, the luminance modulated signals and the color differencemodulated signals can be properly demodulated based on the timing clocksignal superimposed on the audio signal, despite unstable travelingspeed of a cassette tape.

According to a fourth aspect of the invention, there is provided (claim7).

In this aspect, two types of luminance modulated signals read from arecording medium are combined into a luminance signal, while a colordifference modulated signal is halved into two types of color differencesignals.

According to a fifth aspect of the invention, there is provided (claim9).

In this aspect, a color component which is influential in resolution ishalved into first and second separated color component signals each witha lower frequency so that the signal can be recorded in a recordingmedium while maintaining the same information amount. Informationamounts of other color components are reduced before those componentsare combined into a compound color component signal to be recorded in arecording medium.

With this arrangement, image information can be recorded withoutdeterioration of resolution on a recording medium which has limitedcapability of recording an image signal in a high frequency hand byusing an image signal which has been processed to have a lowerfrequency.

According to sixth aspect of the invention, there is provided (claim11).

In this aspect, an image signal is broken up into a plurality of colorcomponents so as to be recorded for every color component. Further, aclock signal having a constant frequency is superimposed onto an audiosignal, and recorded, together with a number or color components, in arecording medium.

With this arrangement, a clock signal for synchronizing reproductiontimings for the respective color component signals can be also recordedin a recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become further apparent from the following description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a block diagram representing a structure of an image signalrecording and reproducing apparatus according to a first preferredembodiment of the present invention;

FIG. 2 is a plan view showing an example structure of a mosaic colorfilter;

FIG. 3 is a diagram illustrating recording status of recording tracks ofa magnetic tape;

FIG. 4 is a diagram illustrating a format for outputting imageinformation to a computer;

FIG. 5 is a block diagram representing a structure of a first digitalprocessor;

FIG. 6 is a diagram expressing positional relationship between a targetpixel and adjacent pixels;

FIG. 7 is a block diagram representing structures of an JPEG encoder anda JPEG decoder;

FIG. 8 is a diagram showing a block structure of a screen to beprocessed according to a JPEG algorithm;

FIG. 9 is a block diagram representing a structure of an image signalrecording and reproducing apparatus according to a second preferredembodiment of the present invention;

FIG. 10A is a block diagram representing structures of clock combiner;

FIG. 10B is a block diagram representing structures of clock separator;

FIG. 11 is a diagram illustrating recording status of recording tracksof a magnetic tape;

FIG. 12 is a block diagram representing a structure of an image signalrecording and reproducing apparatus according to a third preferredembodiment of the present invention;

FIG. 13 is a plan view showing an example structure of a mosaic colorfilter;

FIG. 14 is a diagram explaining an operation timing of a recombiner;

FIG. 15 is a diagram illustrating recording status of a recording trackof a magnetic tape;

FIG. 16 is a block diagram representing a structure of an image signalrecording and reproducing apparatus according to a fourth preferredembodiment of the present invention;

FIG. 17A is a diagram representing structures of a clock combiner;

FIG. 17B is a diagram representing structures of a clock separator;

FIG. 18 is a diagram illustrating recording status of a recording trackof a magnetic tape;

FIG. 19 is a block diagram showing a structure of a conventional imagingdevice; and

FIG. 20 is a diagram explaining an operation timing of a conventionalimaging device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

FIG. 1 is a block diagram representing a structure of an image signalrecording and reproducing apparatus of a first preferred embodiment ofthe present invention.

An image taking unit 10 has the identical structure to that of aconventional imaging device as shown in FIG. 19, comprising a timingcontroller, a driver, and an image sensor. The image sensor accordingto, for instance, QCIF has 176×120 (horizontal×vertical) pixels, andoutputs an image signal I0 for an image picture consisting of 120horizontal lines, each including 176 pixels. The image sensor of theimage taking unit 10 carries a mosaic color filter so that lightreceiving pixel elements of the image sensor are allocated to correspondto color components relative to the color filter. The mosaic colorfilter may comprise, for instance, white (W) segments and green (G)segments alternately arranged in each odd line, and cyan (Cy) segmentsand yellow (Ye) segments in each even line. Therefore, an image signalof an object image taken through the color filter contains colorcomponents corresponding to each segment of the color filter.

An analog processor 11, which operates in synchronism with the outputoperation of the image taking unit 10, performs analog signalprocessing, including sampling, holding, gamma correction, and outputsan image signal I1 according to a predetermined format. For instance, ina sampling and holding operation, an image signal 10 wherein voltagerepeatedly rises/falls to a reset level and to a signal level insynchronism with the output operation of the image sensor, is processedso that voltages at a signal level are solely extracted. Further, in agamma correction operation, the extracted voltage at a signal level isrendered to non-linear conversion for correction of the differencebetween the actual luminance of a reproduced image picture and theluminance thereof perceived by human sight.

An A/D converter 12, which also operates in synchronism with the outputoperation of the image taking unit 10, generates image data D1 byconverting analog image signals I1 supplied from the analog processor 11to digital data. The resultant digital image data D1 each beingoriginated from each light receiving pixel element of the image sensor,indicate the amount of information charges stored in the respectiveoriginated light receiving pixel elements.

A first digital processor 13 executes a predetermined operation to imagedata D1 supplied from the A/D converter 12 to thereby generate red colordata R, blue color data B, and luminance data Y, the luminance databeing a mixture of respective color data at a predetermined ratio. Ingeneration of luminance data Y, color components of the three primarycolors are combined so as to be contained at a predetermined ratio, suchas red:green:blue as 1:2:1, in every data Y on respective lightreceiving pixel elements.

In generation of color data R and B, image data is processed by aconventional color operation every fourth pixel element. For instance,when image data D1 contains color components of yellow (Ye), cyan (Cy),green (G), and white (W) corresponding to the color filter shown in FIG.2, color data (R) is generated by subtracting (G+Cy) from (W+Ye); colordata (G) is generated by subtracting (G+Ye) from (W+Cy). As a result, anamount of luminance data Y equal to the number of light receiving pixelelements installed to the image sensor are generated, along with aquarter as many color data R and B. Further, subtracting luminance datavalue Y from respective color data R and B results in generating colordifference data U and V. In this subtraction, every fourth luminancedata Y is extracted because the number of data R and B each is a quarterof that of luminance data Y. Alternatively, the average of fourluminance data Y is subtracted from the data R and B.

Further, in the first digital processor 13, luminance data Y is oncestored in a buffer before being separated into two groups each includingseparated luminance data in units according to the unit for acompression operation by the JPEG encoder 14 (8 lines×8 columns)(described later). The processor 13 then outputs the two groups ofseparated luminance data in parallel as a pair of separated luminancedata Y1 and Y2. The processor 13 also stores color difference data U andV once in a buffer, and later alternately outputs them as compound colordifference data C in accordance with a processing unit for a compressionoperation by the JPEG encoder 14.

Note that, since the amount of color difference data U, V each are botha quarter of that of luminance data Y, separated luminance data Y1, Y2and compound color difference data C are resultantly outputlly at thesame rate. Also, in the processor 13, one image picture (an image forone screen) is divided into a plurality of blocks each consisting of 8lines×8 columns pixels, and respective data is outputted by the unit ofa block. With this arrangement, outputted data can be adopted to acompression operation by the JPEG encoder 14.

The JPEG encoder 14 performs a compression operation according to JoinPhotographic Expert Group (JPEG) with respect to separated luminancedata Y1, Y2 and compound color difference signals C supplied in blocksfrom the first digital processor 13. The compression operation isconducted individually for these data, either via three circuits inparallel or via one circuit operating in a time division method. As aresult of this operation, the separated luminance data Y1, Y2, andcompound color difference data C are respectively transformed intocompressed luminance data y1, y2, and compressed color difference dataC.

A modulator 15 gives analog modulation to compressed luminance data y1,y2 and compressed color difference data c output from the JPEG encoder14, and supplies resultant signals capable of being recorded in magneticrecording media, namely luminance modulated signal m1, m2, and colordifference modulated signal mc, to a recording/reproducing section 16.The modulator 15 also gives analog modulation to sound data S whichcorresponds to an audio signal generated during an image takingoperation by the image taking unit 10, and supplies the resultantsignal, or a sound modulated signal mS, to the recording/reproducingsection 16.

Sound data is obtained via a microphone (not shown) or the like, whichis generally provided together with the image taking unit 10. As thesound data S has a smaller amount of information compared to luminancedata Y or other data, it may be supplied intact to analog modulationwithout being compressed. Also, sound data S may be supplied in the formof an analog data to the recording and recording section 16, withoutbeing converted into digital data.

The recording/reproducing section 16 receives luminance modulatedsignals m1, m2, color difference modulated signal mc, and soundmodulated signal mS from the modulator 15, and writes them into fourrecording tracks of a magnetic tape 20 by using a magnetic head 17connected thereto. For instance, as shown in FIG. 3, luminance modulatedsignals m1, m2 are recorded in the first and second recording tracks forevery block (64 pixels), while color difference modulated signal mc isrecorded in the third recording track. Note that, in this recording, acolor difference modulated signal mc corresponding to the first colordifference data U, namely signal mc-U, and that corresponding to thesecond color difference data V, namely a signal Mc-V, are recordedalternately for every block. Finally, a sound modulated signal mS iscontinuously recorded in the fourth recording track.

While recording these modulated signals m1, m2, mc, mS, therecording/reproducing section 16 also reads recorded modulated signalsm1, m2, mc, mS from a magnetic tape 20, as the section 16 is constructedso as to read these signals recorded in the magnetic tape 20 by usingthe magnetic heat 17, and supply them to a de-modulator 21 in the imagereproduction mode. That is, the section 16 performs either a writing orreading operation using modulated signals m1, m2, mc, mS with respect tothe magnetic tape 20 according to an operation mode desirably switched.

The de-modulator 21 gives a decoding operation with respect toreproduced signals input in four separate lines from the section 16 tothereby restore digital data of compressed luminance data y1, y2,compressed color difference data c, and sound data S. Compressedluminance data y1, y2 and compressed color difference data c are thensupplied to a JPEG decoder 22 (described later), while sound data S issupplied to an audio reproduction system (not shown) including a D/Aconverter, an amplifier, and so on.

A JPEG decoder 22, which operates inversely to the JPEG encoder 14,gives a decoding operation to compressed luminance data y1, y2 andcompressed color difference data c supplied from the de-modulator 21 tothereby restore separated luminance data Y1, Y2 and compound colordifference data C. The restored data are for the most part identical tothose generated by the digital processor 13, depending on thecompression rate set with the JPEG encoder 14. Similar to the JPEGencoder 14, compressed luminance data y1, y2, and compressed colordifference data c are individually processed by three separate, parallelcircuits or one circuit operating according to a time division method.

A second digital processor 23 stores in a buffer, separated luminancedata Y1, Y2 supplied in blocks by the JPEG decoder, and combines thedata Y1 and Y2 into luminance data Y in one successive line. Theprocessor 23 also divides compound color difference data C in blocksinto color difference data U and V each in successive lines. Theprocessor 23 supplies the resultant luminance data Y and the colordifference data U, V to a computer device according to a predeterminedformat, as well as to a display 24. With the above, an image read fromthe magnetic tape 20 can be displayed on a monitor.

In supplying image information to a computer device, 411 format and 422format are available. In 411 format, luminance information and two colordifference information are combined at the ratio 4:1:1; in 422 format,at 4:2:2.

With 411 format, as shown in FIG. 4, luminance data Y of 8 bits isforwarded for every 8 bits, or one pixel, in one forwarding cycle, whilecolor difference data U, V each of 8 bits is forwarded for every twobits in one forwarding cycle. That is, while one luminance data y (8bits) is forwarded in one forwarding cycle, a pair of color differencedata U, V are forwarded in four cycles, i.e., 2×2 bits in one cycle.

With this forwarding operation, one pair of color difference data valuesU, V and four luminance data point Y are forwarded using a transmissionline of 12 bits.

Note that the luminance data Y and color difference data U, V generatedby the second digital processor 23 can be supplied intact to a computerdevice according to 411 format, as the data contains luminanceinformation and two color difference information in the 4:1:1 ratio.

With 422 format, as shown in FIG. 4, luminance data of 8 bits for onepixel is forwarded for every pixel in one forwarding cycle, while twotypes of color difference data U, V, each of 8 bits for one pixel, arealternately forwarded for every one pixel. In 422 format in whichluminance data Y and two types of color difference data U and V arerequired to be combined at the ratio 4:2:2, the number of colordifference data U, V must be doubled through interpolation betweenadjacent pixels using their average value.

Data transmission rates at respective sections under QCIF Standards willnext be explained.

An image picture according to QCIF Standards must consist of 176×120(horizontal×vertical) pixels. Providing that image data D1 representsone pixel by using eight bits, the total data amount for one imagepicture is

    176×120×8=168.96 Kb.

Given a frame rate of 1/15 second, the image data D1 is input into thefirst digital processor 13 at a transmission rate of

    168.96K×15=2534.4 Kbps.

Since the amount of luminance data Y equals that of image data D1, whilecolor difference data U, V each have a quarter the amount of data of theluminance data Y, the amount of data being outputted from the firstdigital processor 13 will be 1.5 times as large as that which has beinginputted thereto. This data with an increased amount is output via threetransmission paths to the JPEG encoder 14 at a transmission rate of

    2534.4K×1.5/3=1267.2 Kbps.

Providing that a compression rate of the JPEG encoder is 1/30, the abovedata is input into the modulator 15 at a transmission rate of

    1267.2K/30=42.24 Kbps.

When speaking of an analog signal which is capable of expressing twodigital data in one cycle, 2 bps substantially corresponds to 1 Hz.Therefore, respective modulated signals m1, m2, mc to be inputted intothe recording/reproducing section 16 each have a frequency of

    42.24K/2=21.12 Khz.

A common audio cassette tape is generally usable with a frequency bandup to around 20 KHz, is able to record respective modulated signal m1,m2, mc because although the above frequency was calculated under theassumption that 176×120 pixels are all effective, most of the time inactuality, not all pixels are used as some peripheral pixels are locatedout of the effective image region. Therefore, the amount of data for oneimage picture turns out to be less than that on which the abovecalculated is based, and the frequency of respective modulated signalsm1, m2, mc resultantly drop under 20 KHz, even if the frame rate of theimage taking unit 10 is equal to the compression rate of the JPEGencoder 14.

FIG. 5 is a block diagram representing an example structure of the firstdigital processor 13.

The first digital processor 13 comprises a luminance calculator 31, anoutline corrector 32, a separator 33, a color calculator 34, a colordifference calculator 35, and a combiner 36.

The luminance calculator 31 adds image data D1 of the pixels surroundinga target pixel to image data D1 of the target pixel at a predeterminedratio, to thereby generate luminance data Y containing color componentsof three primary colors (R, G, B) at 1:2:1. For instance, as shown inFIG. 6, the image data D1 of the target pixel T is combined byrespective halves of image data D1 of the four adjacent pixels, i.e., onthe upper, lower, left, and right sides, (A2, B2, C1, C2), and quartersof image data D1 of four diagonally adjacent four pixels (A1, A3, B1,B3) to thereby generate luminance data Y. By making the abovecalculation corresponding the color filter shown in FIG. 2, arelationship of

    W+G+Ye+Cy=2R+4G+2B=Y

is obtained for all pixel elements, so that luminance data Y containingcolor components of red, green, and blue at 1:2:1 is obtained.

The outline corrector 32 generates luminance data Y' with enhancedcontrast by adding to the luminance data Y of the target pixel, thedifference in luminance data Y of between the target pixel and theadjacent pixels. For example, as shown in FIG. 6, a value obtained byaveraging the differences in luminance data Y between the target data Yand the respective upper, lower, right, and left pixels (A2, B2, C1,C2), and then amplifying by a predetermined factor, is added to theluminance data Y of the target pixel T.

The separator 33 rearranges the luminance data Y' supplied by the rasterunit, or in successive lines, into successive blocks each of 8×8 pixels,which are then alternately extracted to be arranged in two groups, i.e.,first and second luminance data Y1 and Y2, and output.

The above rearrangement, i.e., raster/block conversion, is done becauseluminance data Y' supplied from the outline corrector 32 in successivelines corresponding to horizontal scanning by the image sensor, must berearranged to be in successive blocks each of 8 lines×8 columns to beapplicable to the compression operation by the JPEG encoder 14. Further,in order to avoid loss accompanying a lowering of transmission rate, theluminance data Y' in successive blocks are divided into two successivelines of blocks, one including odd-numbered blocks, or first separatedluminance data Y1, and the other even-numbered blocks, or secondseparated luminance data Y2, so that they can be output via twotransmission lines.

The color calculator 34 takes image data D1 for every four pixels suchthat each data D1 contains different color components, and conducts apredetermined color calculation to thereby generate color data Rcorresponding to red color components and color data B corresponding toblue color components. For instance, when using a color filter shown inFIG. 2, in which four mutually adjacent pixels respectively correspondto colors W, G, Ye, Cy, color data R and B will be generated in thefollowing calculation. That is, the color data R is generated bysubtracting the sum of image data D1 of colors G and Cy, i.e., (G+Cy),from the sum of image data D1 of colors W and Ye, i.e., (W+Ye); thecolor data B is generated by subtracting the sum of image data D1 ofcolors G and Ye, i.e., (G+Ye), from the sum of image data D1 of colors Wand Cy, i.e., (W+Cy).

The color difference calculator 35 generates color difference data U, Vby subtracting luminance data Y supplied from the luminance calculator31 from color data R and B supplied from the color calculator 34. Notethat the color calculator 35 takes either luminance data Y for everyfourth data, or the average of the four luminance data Y in the abovesubtraction operation, as the numbers of color data R, B each are aquarter of that of luminance data Y.

The combiner 36 rearranges the color difference data U, V supplied bythe raster unit, or in successive lines, into being arranged insuccessive blocks each of 8 lines×8 columns. The combiner 36 furtherextracts color difference data U in blocks and color difference data Vin blocks, and alternately combines them thereby generating a compoundcolor difference data C to output.

The rearrangement i.e., raster/block conversion, is dones because colordifference data U, V supplied by the color calculator 35 in successivelines corresponding to horizontal scanning by the image sensor, must berearranged to be in successive blocks each of 8 lines×8 columns so thatcompression by the JPEG encoder can be applied. Further, the combiner 36alternately outputs color difference data U as odd-numbered blocks andcolor difference data V as even-numbered blocks at a transmission ratematching that of the separated luminance data Y1, Y2.

Note that the first digital processor 13 is connected to a RAM which iscommonly accessible from the respective circuits 31 to 36, the RAM beingcapable of storing data for an appropriate number of lines to be neededin the respective circuits 31 to 36.

FIG. 7 is a block diagram representing structures of the JPEG encoderand the JPEG decoder 22 for processing separated luminance data Y1. AJPEG encoder and a JPEG decoder having identical structures will be alsoused for separated luminance data Y2 and compound color difference dataC.

In an encoding format according to JPEG algorithm, one image picture isdivided into a plurality of blocks each consisting of 8×8 pixels, asshown in FIG. 8, and an encoding operation is conducted for every block.That is, 64 data P11 to P88, constituting one block of 8 lines×8columns, is used as one unit for an encoding operation so that theamount of data is reduced.

The JPEG encoder 13 comprises a DCT circuit 41, a quantizing circuit 42,and an encoder 43, while the JPEG decoder 22 comprises a decoder 44, aninverse quantizing circuit 45, and an IDCT circuit 46. The JPEG encoder13 and the JPEG decoder 22 are connected to a quantization table storingthreshold values for quantizing/inverse quantizing operations, and to anencoder table 48 storing Huffuman codes for encoding/decodingoperations.

The DCT circuit 41 takes in separated luminance data Y1 for one block (8lines×8 columns=64 pixels), and performs second order discretion cosinetransform (DCT) with respect to the taken image data Y1 to therebygenerate 64 DCT factors.

The quantizing circuit 42 quantizes the DCT factors supplied by the DCTcircuit 41 while referring to threshold values stored in thequantization table 47. The threshold, which is defined according to thepurpose of the device, is used in a quantizing operation to determinethe compression rate for image data and the image quality of reproducedimages. The encoder 43 performs a variable length encoding operation toa quantized DCT factor, based on the Huffuman code stored in theencoding table 48, to thereby generate compressed luminance data y1. TheHuffuman codes are codes having a variable length, and assignedbeforehand to quantized DCT factors according to the expected frequencyin being used. As a frequently used quantized DCT factor is given ashort Huffuman code, using an JPEG encoder enables compression of thedata amount to about 1/40.

Inversely from the encoder 43, the decoder 44 takes compressed luminancedata y1 for one block (8 lines×8 columns=64 pixels), and performs avariable length decoding operation to compressed image luminance data,based on the Huffuman code stored in the encoding table 48. Note that afactor obtained through a variable length decoding operation correspondsto a quantized DCT factor obtained by the JPEEG encoder 13. Inverselyfrom the quantizing circuit 42, the inverse quantizing circuit 45performs an inverse quantizing operation with respect to a factorsupplied by the decoder 44, referring to a threshold value stored in thequantization table 47, to thereby restore a DCT factor. Then, the IDCTcircuit 46 performs inverse discrete cosine transform (IDCT) withrespect to a DCT factor supplied by the inverse quantizing circuit 45 tothereby restore separated luminance data Y1. In the IDCT circuit 46,data for one block is simultaneously converted before being sequentiallyoutputted for every pixel in a predetermined order.

In the above, an image signal according to QCIF Standards have beendescribed. It is, however, not limited to QCIF Standards, and anystandards defining the size up to that of CIF Standards may beapplicable in recording image signals in magnetic recording media, suchas an audio cassette tape. Also, data compression algorithms other thanJPEG, such as MPEG or H.263, may be used instead.

As described above, according to this embodiment of the invention, it ispossible to record and reproduce an image signal for color images on asimple structure using an audio cassette tape. Thus, there can beprovided a low cost imaging device, with able to record and reproduce animage signal for displaying a picture small enough to be used with acomputer device.

Embodiment 2

FIG. 9 is a block diagram representing a structure of an image signalrecording/reproducing apparatus according to the second preferredembodiment of the present invention.

An image taking unit 110 has the identical structure to that of aconventional image taking unit as shown in FIG. 19, comprising a timingcontroller, a driver, and an image sensor. The image sensor whichaccords to, for instance, QCIF, has 176×120 (horizontal×vertical) pixelsattached thereto, and outputs an image signal I0 for an image pictureconsisting of 120 horizontal lines, each including 176 pixels. The imagesensor of the image taking unit 110 carries a mosaic color filter sothat light receiving pixel elements attached to the image sensor areallocated to correspond to color components relative to the colorfilter. The mosaic color filter may comprise, for example, white (W)segments and green (G) segments alternately arranged in each odd line,and cyan (Cy) segments and yellow (Ye) segments in each even line.Therefore, a resulting image signal contains color componentscorresponding to each segment of the color filter.

The operations of analog processor 111, A/D converter 112, first digitalprocessor 113, JPEG encoder 114 are the same as described in the firstpreferred embodiment and therefore will not be described again here.

A modulator 115 operates in the same manner as described in the firstembodiment. That is, it gives analog modulation to compressed luminancedata y1, y2 and compressed color difference data c outputted from theJPEG encoder 114, and supplies resultant signals capable of beingrecorded in magnetic recording media, namely luminance modulated signalm1, m2, and color difference modulated signal mc, to arecording/reproducing section 116.

In this modulator 115, arrangement of "1" and "0" in digital data istransformed through analog modulation to be expressed by means ofamplitudes of an analog signal, wherein one cycle of each modulatedsignal represents data for two bits.

A sound transmitter 120, including a microphone and an amplifier,records sound occurring when taking object images, and outputs thissound as an audio signal S. The sound transmitter 120 is generallyprovided together with the image taking unit 110.

A clock combiner 118 comprises a low pass filter 118a and an adder 118b,as shown in FIG. 10(a). The combiner 118 obtains, through the low passfilter 118a, the audio signal S0 input from the sound transmitter 120,and superimposes a common reference clock CK onto the audio signal S0using the adder 118b to thereby generate a composite audio signal S1 tooutput. Note that a reference clock CK is synchronized with the timingat which imaging at which compressed luminance data y1, y2, andcompressed color difference data are output from the JPEG encoder 114,and also the timing at which luminance modulated signals m1, m2, andcolor difference modulated signal mc are output from the recording andreproducing section 116.

When the low pass filter 118a is set to have a 10 KHz cut-off frequency,a listener can hear the sounds reproduced from signals having passedthrough the filter without loss of quality because the human ear canusually not discern frequency components above 10 KHz. While the cut-offfrequency for the low pass filter is thus set at 10 KHz, a referenceclock CK has a frequency of about 20 KHz, similar to luminance modulatedsignals m1, m2, and color difference modulated signal mc (describedlater). Therefore, frequency bands of an audio signal S0 and of areference clock CK can be separated.

The recording/reproducing section 116 receives luminance modulatedsignals m1, m2, color difference modulated signal mc, and soundmodulated signal mS from the modulator 115, and a composite signal S1from the clock combiner 118, and writes them onto four recording tracksof a magnetic tape 120 through a magnetic head 117. For example, asshown in FIG. 12, luminance modulated signals m1, m2 are recorded in thefirst and second recording tracks for every block (64 pixels), whilecolor difference modulated signal mc is recorded in the third recordingtrack. Note that, in this recording, a color difference modulated signalmc corresponding to the first color difference data U, namely signalmc-U, and that corresponding to the second color difference data V,namely a signal Mc-V, are recorded alternately for every block. Finally,a composite audio signal S1 including a reference clock CK iscontinuously recorded in the fourth recording track.

While recording modulated signals m1, m2, mc, and a composite audiosignal S1, the recording/reproducing section 16 also reads recordedmodulated signals m1, m2, mc, a composite audio signals S1, as thesection 116 is constructed so as to read those signals recorded in themagnetic tape 130 using the magnetic head 117, and supply them to ademodulator 121 and a clock separator 125 in the image reproductionmode. That is, the section 16 performs either a writing or readingoperation using modulated signals m1, m2, mc, and a composite audiosignals S1 with respect to the magnetic tape 130 according to anoperation mode desirably switched.

Demodulator 121 gives a decoding operation with respect to thereproduced signals supplied via three separate lines from the section116 to thereby restore digital data of compressed luminance data y1, y2and compressed color difference data c. In other words, the demodulator121 demodulates modulates signals m1, m2, mc, based on a reference clockCK supplied from the clock separator 125. As a result, inverseprocessing to the modulating processing by the modulator 115 is properlyachieved regardless of fluctuation in the traveling speed of themagnetic tape 130.

The operations of a JPEG decoder 122 and a second digital processor 123are the same as described in the first preferred embodiment and will notbe described again here.

A clock separator 125 comprises a low pass filter 125a and a high passfilter 125b, as shown in FIG. 10B. The separator 125 extracts from acomposite audio signal S1 supplied by the recording/reproducing section116, an audio signal S0 through the low pass filter 125a, and areference clock CK through the high pass filter 125b. The cut-offfrequency of the low pass filter 125a is set equal to that of the clockcombiner 118a of the clock combiner 118, while that of the high passfilter 125b is set higher than that of the low pass filter 118a of theclock combiner 118 and lower than the frequency of the reference clockCK. For instance, providing that the cut-off frequency of the low passfilter 118a is set at 10 KHz and the frequency of a reference clock CKis 20 KHz, the cut-off frequency of the low pass filter 125a is set at10 KHz and that of the high pass filter 125b is 15 KHz.

A sound reproducer 126 comprises an amplifier and a speaker, andreproduces sounds via the speaker in response to an audio signal S0(excluding 10 KHz or more frequency components) which has been deprivedof a reference clock by the clock separator 125. With this operation,sounds can be reproduced accompanying image displaying by the displaydevice 124.

Data transmission rates at respective sections under QCIF Standards weredescribed in the first preferred embodiment and will not be repeatedhere.

Also as described in the first embodiment, the respective modulatedsignals m1, m2, mc to be supplied to the recording/reproducing 116 eachhave a frequency of

    43.24K/2=21.12 KHz.

An audio cassette tape, which is generally usable with a frequency bandup to around 20 KHz, is nevertheless able to record these signals, evenif the frame rate of the image taking unit 10 is equal to thecompression rate of the JPEG encoder 14, as described in the firstembodiment.

In the above, an image signal according to the QCIF standard has beendescribed. The applicable standard is, however, not limited to QCIF, andany standard defining a size up to that of CIF may be used in recordingimage signals in magnetic recording media, such as a conventional audiocassette tape. Also, data compression algorithm other than JPEG, such asMPEG or H.263, may be used instead.

As described above, according to this embodiment of the presentinvention, it is possible to record and reproduce an image signal forcolor images on a simple structure using an audio cassette tape. Thus,there can be provided a low cost imaging device capable of recording andreproducing an image signal for displaying a small picture on a computerdevice.

Embodiment 3

FIG. 12 is a block diagram representing a structure of an image signalrecording and reproducing apparatus of a third preferred embodiment ofthe present invention.

An imaging unit 210 has the structure of that of a conventional imagetaking unit as shown in FIG. 19, comprising a timing controller, adriver, and an image sensor. An image sensor complying to, for example,the QCIF standard, has 176×120 (horizontal×vertical) pixels attachedthereto, and outputs an image signal I0 for an image picture consistingof 120 horizontal lines, each including 176 pixels. The image sensor ofthe image taking unit 210 carries a color filter. This color filter may,for example, be stripe, as shown in FIG. 13, in which lines of yellow(Ye), green (G), and cyan (Cy) segments are repeatedly arranged.Therefore, an image signal passing through the filter contains colorcomponents corresponding to each segment of the color filter. Asample/hold circuit 211 samples an image signal I0 supplied from animage taking unit 210, at a timing according to an output operation ofthe unit 210, and outputs an image signal I1. That is, an image signalI0 wherein voltage repeatedly rises/falls to a reset level and a signallevel in synchronism with the output operation of the image sensor ofthe image taking unit 210, is processed by the sample/hold circuit 211such that voltages at a signal level are extracted, thereby obtaining animage signal I1 wherein voltage remains at a signal level.

An automatic gain controller 212 amplifies the image signal I1 suppliedfrom the sample/hold circuit 211 such that the average (signal voltage?) level during a certain period of time remains within a predeterminedrange, and outputs an image signal I2.

A gamma corrector 213 performs non-linear conversion with respect to theimage signal I2 supplied from the automatic gain controller 212, andoutputs an image signal I3. Non-linear conversion is made to correct alinear distortion perceived by human sight in order to generate an imagesignal I3 with a linear distortion corrected.

A color dissolver 214, which operates in synchronism with an outputoperation of the image taking unit 210, dissolves the image signal I3into respective color components. For instance, when using a stripedcolor filter as shown in FIG. 14, an image signal I3 is dissolved (in apredetermined manner) during three cycles, thereby generating colorcomponent signals C1, C2, C3 respectively corresponding to colorcomponents Ye, G, Cy. The color dissolver 114 maintains a constantvoltage during the cycles for dissolution (for instance, a three-clockperiod). With this dissolution, each frequency of the color componentssignals C1, C2, C3 is reduced to one third of that of the image signalI3.

A recombiner 215 combines color component signals C1, C2, C3 suppliedfrom the color dissolver 214 to thereby generate two types of separatedcolor component signals Ca and Cb and a compound color component signalCc. Signals Ca and Cb are formed by halving a color component signal C2corresponding to a color component G; a signal Cc is formed bycompounding color component signals C1 and C3 respectively correspondingto color components Ye and Cy.

Specifically, in the circuit 215, color component signals C2, whichcorrespond to color components G which are influential in a luminancesignal, are extracted from all lines without being compressed, andseparated into odd-numbered segments and even-numbered segments torespectively constitute color component signals Ca and Cb. Moreover,color components signals C1, C3, respectively correspond to colorcomponents Ye and Cy, which are less influential in a luminance signalas compared to color components G, are extracted for every other line,and alternately connected together to constitute a compound colorcomponent signal Cc. For instance, when using a staiped color filter asshown in FIG. 13, color component signals C1, C2, C3 are supplied inlines to the re-combiner 215. Then, signal C2 is divided into twogroups, one for the odd-numbered segments (Gn-odd) and the other foreven-numbered segments (Gn-even) which respectively constitute two typesof separated color components signals Ca, Cb. Further, color componentsignals C1 and C3 are extracted from the respective odd-numbered andeven-numbered lines, and alternately connected together as respectiveodd-numbered (Yen-odd) and an even-numbered (Cyn-even) color components.The connected color components constitute a compound color componentsignal Cc. With this operation, each frequency of the separated colorcomponent signals Ca, Cb and a compound color component signal Cc hasbeen lowered to a half of that of the color component signals C1, C2,C3.

The recording/reproducing section 216 receives separated color componentsignals Ca, Cb and a compound color component signal Cc from there-combiner 215, and writes them onto a magnetic tape 220 throughmagnetic head 217. The magnetic tape 220 has three or more recordingtracks so as to record, for instance, independently the first and secondseparated color components signals Ca, Cb and a compound color componentsignal Cc in lines. Note that, in the third recording track, yellowcolor components (Cc-Ye) and cyan color components (Cc-Cy) arealternately recorded, corresponding to the compound color componentsignal C.

While recording these separated color component signals Ca, Cb and acompound color component signal Cc, the recording/reproducing section216 also reads recorded separated color component signals Ca, Cb and acompound color component signal Cc, as the section 216 is constructed soas to read these signals Ca, Cb, Cc recorded in the magnetic tape 220through magnetic head 217, and supply them to a clumping circuit 221 inthe image reproduction mode. That is, the section 216 performs either awriting or reading operation using separated color component signals Ca,Cb, and a compound color component signal Cc with respect to themagnetic tape 220 according to an operation mode desirably switched.

A clumping circuit 221 performs a clumping operation at a referencelevel with respect to every line of separated color component signalsCa, Cb and a compound color component signal Cc supplied from the sector16. That is, a voltage of the signals Ca, Cb, Cc is fixed at apredetermined value during a period provided either at the beginning orend of each line of the signals, whereby the voltage levels of thesignals Ca, Cb, Cc are stabilized, the voltage level during the periodbeing regarded as a reference level.

A color matrix circuit 222 performs a matrix operation with respect tothe separated color component signals Ca, Cb and a compound colorcomponent signal Cc supplied from the clumping circuit 221 to therebygenerate a luminance signal Y and color difference signals R-Y, B-Y.That is, all color components contained in the separated color componentsignals Ca, Cb, and the compound color component signal Cc are summed upwhereby a luminance signal Y is generated which contains the threeprimary color components, i.e., red (R), green (G), and blue (b)combined at the ratio 1:3:1. Also, color component R is generated bysubtracting color components G from color components Ye; colorcomponents B is generated by subtracting color components G from colorcomponents Cy. Still further, color difference signals (R-Y) and (B-Y)are generated through subtraction of a luminance signal respectivelyfrom color components R and B. Note that, as to a compound colorcomponent signal Cc, a conventional delay line is employed so that linesfor color components Ye and Cy can appear simultaneously at every line,as each line otherwise represents only one of a color component Ye orCy.

A digital processor 223 gives digital conversion to a luminance signal Yand color difference signals R-Y, B-Y supplied from the color matrixcircuit 222, as well as a filtering operation for outline correction andother operations for color balance adjustment. With these operations,luminance data Y0 and color difference data U, V are generated. Notethat the luminance signal Y and color difference signals R-Y, B-Y mayalso be supplied to an external device. The digital processor 223supplies resultant luminance data Y0 and color difference data U, V to acomputer device in a predetermined format, as well as to a displaydevice 224. With the above, an image read from the magnetic tape 220 canbe displayed on a monitor.

Here, frequencies of respective signals according to QCIF Standards willbe discussed.

An image picture according to QCIF Standards must consist of 176×120(horizontal×vertical) pixels. Given a frame rate of 1/15 seconds, animage signal I0 has a frequency of

    176×120×15=316.8 KHz,

which is common to image signals I0 to I3. At the color dissolver 14,where an image signal I3 is dissolved into three components, namelycolor component signals C1, C2, C3, those divided signals each have afrequency of

    316.8/3=105.6 KHz.

Further, at a re-combiner 215, where a color component signal C2 ishalved into separated color component signals Ca, Cb, and colorcomponent signals C1, C2 are curtailed to be one second, the resultantsignals, namely, signals, Ca, Cb, Cc, each have a frequency of

    105.6/2=52.8 KHz.

A common audio cassette tape, which is generally usable with a frequencyband up to around 20 KHz, is able to record separated color componentsignals Ca, Cb and a compound color component signal Cc having the abovecalculated frequency when the tape is driven at three times its normalspeed.

In the above, an image signal according to QCIF Standards have beendescribed. It is, however, not limited to QCIF, and any standarddefining a size up to that of CIF may be applicable in recording imagesignals in magnetic recording media, such as an audio cassette tape.Also, data compression algorithm other than JPEG, such as MPEG or H.263,may be used instead.

As described above, according to this embodiment of the presentinvention, it is possible to record and reproduce an image signal forcolor images on a simple structure using an audio cassette tape. Thus,there can be provided an imaging device, with a small cost, forrecording and reproducing an image signal for displaying a picture smallenough to be taken into a computer device.

Embodiment 4

FIG. 16 is a block diagram representing a structure of a fourthpreferred embodiment of the present invention.

The structure from sample/hold circuit 211 to the color dissolver 214,and that from the clumping circuit 221 to the display device 224 areidentical to those shown in FIG. 13 for the third preferred embodiment.In this embodiment, a sound transmitter 230 for outputting an audiosignal is connected so that an audio signal is recorded in a magnetictape 220 together with separated color component signals Ca, Cb and acompound color component signal Cc.

A sound transmitter 230, including a microphone and an amplifier,gathers sound when recording object images, and outputs the sound as anaudio signal S0. The sound transmitter 230 is generally providedtogether with the imaging unit 210.

A clock combiner 231 comprises a low pass filter 231a and an adder 231b,as shown in FIG. 17A. The combiner 231 obtains, through the low passfilter 231a, the audio signal S0 input from the sound transmitter 230,and superimposes by using the adder 231b a common reference clock CKonto the audio signal S0, to thereby generate a composite audio signalS1 to output. A reference clock CK is in synchronism with an outputoperation of a re-combiner 215, and also with separated color differencecomponent signals Ca, Cb and a compound color component signal Cc.

When the low pass filter (218a ?) is set to have a 10 KHz cut-offfrequency, listeners can hear the sounds reproduced from signals havingpassed through the filter without difficulty because most human ears cannot hear frequency components greater than 10 KHz. While the cut-offfrequency for the low pass filter is thus set at 10 KHz, a referenceclock CK has a frequency of about 52.8 KHz, similar to separated colorcomponent signals Ca, Cb and a compound color component signal Cc.Therefore, frequency bands of an audio signal S0 and a reference clockCK can be separated.

Similar to the structure shown in FIG. 12, a recombiner 215a combinescolor component signals C1, C2, C3 to thereby generate two types ofseparated color component signals Ca and Cb, and a compound colorcomponent signal Cc. In this process, a vertical synchronizing signal VDand a horizontal synchronizing signal HD are superimposed onto any ofthe separated color component signals Ca, Cb, or a compound colorcomponent signal Cc during the blanking periods. For instance, avertical synchronizing signal VD for determining a vertical scanningtiming with an image signal I0, is superimposed onto a separated colorcomponent signal Ca during the blanking period thereof, while ahorizontal synchronizing signal HD for determining a horizontal scanningtiming is superimposed onto a separated color component signal Cb duringthe blanking period thereof. That is, with superimposition of verticaland horizontal synchronizing signals VD and HD onto two types ofindependent separated color component signals Ca, Cb, separation ofvertical and horizontal scanning signals is unnecessary.

The recording/reproducing section 216a receives composite audio signalS1 from the clock combiner 231, and separated color component signalsCa, Cb, and a compound color component signal Cc from the re-combiner215a, and writes them in parallel onto the four recording tracks of amagnetic tape through magnetic head 217. For example, as shown in FIG.18, the separated color components signals Ca, Cb are recorded in thefirst and second recording tracks, respectively; a compound colorcomponent signal Cc is recorded in the third recording track; and acomposite audio signal S1 is continuously recorded in the fourthrecording track.

While recording these separated color component signals Ca, Cb, acompound color component signal Cc, and a composite audio signal S1, therecording/reproducing section 216a also reads recorded separated colorcomponent signals Ca, Cb, a compound color component signal Cc, and acomposite audio signal S1. The read separated color component signalsCa, Cb and a compound color component signal Cc are supplied to theclumping circuit 221, while the composite audio signal S1 is supplied tothe clock separator 232.

A clock separator 232 comprises a low pass filter 125a and a high passfilter 125b, as shown in FIG. 17B. The separator 25 extracts from acomposite audio signal S1 supplied by the recording/reproducing section216a, an audio signal S0 through the low pass filter 232a, and areference clock CK through the high pass filter 232b. The cut-offfrequency of the low pass filter 232a is set equal to that of the clockcombiner 231a, while that of the high pass filter 232b is set higherthan that of the low pass filter 232a and lower than the frequency ofthe reference clock CK. For instance, providing that the cut-offfrequency of the low pass filter 231a is set at 10 KHz and the frequencyof a reference clock CK is 53 KHz, the cut-off frequency of the low passfilter 232a is set at 10 KHz and that of the high pass filter 232b is at20 KHz. The reference clock CK extracted by the clock separator 232, issupplied to the color matrix circuit 222 to be referred to in a matrixoperation.

The color matrix circuit 222 is able to perform a matrix operation basedon a vertical synchronizing signal VD and a horizontal synchronizingsignal HD superimposed onto any of the separated color component signalsCa, Cb, and a compound color component signal Cc during the blankingperiods. Thus, erroneous operation due to unmatched timing can beprevented.

The sound reproducer 233 comprises an amplifier and a speaker, andreproduces sounds via the speaker in response to a audio signal S0(excluding 10 KHz or more frequency components) which has been deprivedof a reference clock by the clock separator 125. With this operation,sound reproduction is achieved accompanying image displaying by thedisplay device 224.

In the fourth preferred embodiment, a composite audio signal S1including a reference clock CK is recorded on a recording media, or amagnetic tape 220, together with separated color component signals Ca,Cb and a compound color component signal Cc. With this arrangement,reproduction (?) timings for separated color component signals Ca, Cband a compound color component signal Cc can be easily synchronized atthe time of image reproduction.

In the above, an image signal according to the QCIF standard have beendescribed, however, any standards defining a size up to that of the CIFstandard may be used to record image signals in magnetic recordingmedia, such as an audio cassette tape. As described in the above,according to the present invention, it is possible to record andreproduce an image signal for color images on a simple structure usingan audio cassette tape. Thus, there can be provided a low cost imagingdevice, for recording and reproducing an image signal for displaying asmall picture suitable for computer devices.

Further, since a reference clock is superimposed on an audio signal soas to be recorded together with an image signal, it is possible to makeimage and audio signals to be synchronized at the time of imagereproduction, so that an image signal can be accurately reproduced, evenif the traveling speed of a reproduction mechanism is rather unstable.

While there have been described what are at present considered to bepreferred embodiments of the invention, it will be understood thatvarious modifications may be made thereto, and it is intended that theappended claims cover all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:
 1. An image signal recording and reproducingapparatus for recording an image signal in a recording medium having aplurality of recording tracks, the image signal corresponding tosuccessive images screen by screen, comprising:a supplier forcontinuously supplying image data corresponding to the image signal, theimage data individually representing a plurality of pixels eachresponsible for a specific color component; a processor for generatingluminance data for each pixel, based on the image data,outputting inparallel a pair of separated luminance data obtained by halving theluminance data generated, generating two types of color difference dataeach corresponding to four pixels, based on the image data, andoutputting a compound color difference data obtained by alternatelycombining the two types of color difference data generated, by apredetermined unit; a compressing encoder for generating a pair ofcompressed luminance data and a compressed color difference data bygiving a compressing operation to the pair of separated luminance dataand the compound color difference data according to a predeterminedalgorithm; a modulator for generating a pair of luminance modulatedsignals and a color difference modulated signal by giving an analogmodulating operation to the pair of compressed luminance data and thecompressed color difference data; and a recorder for writing the pair ofluminance modulated signals and the color difference modulated signalonto first to third parallel recording tracks of the recording medium.2. An image signal recording and reproducing apparatus according toclaim 1, wherein:the recorder writes an audio signal corresponding tothe image signal onto a fourth recording track of the recording medium.3. An image signal recording and reproducing apparatus according toclaim 1, further comprising:a reproducer for reading a pair of luminancemodulated signals and a color difference modulated signal respectivelyfrom the first to third recording tracks of the recording medium; ademodulator for generating a pair of compressed luminance data andcompressed color difference data by giving a demodulating operation tothe pair of luminance modulated signals and the color differencemodulated signal; and an expanding decoder for restoring a pair ofseparated luminance data and compound color difference data by giving anexpanding operation according to an identical algorithm employed by thecompressing encoder, to the pair of compressed luminance data and thecompressed color difference data.
 4. An image signal recording andreproducing apparatus according to claim 3, wherein:the recorder writesan audio signal corresponding to the image signal onto the fourthrecording track of the recording medium, and the reproducer reads theaudio signal from the fourth track of the recording medium.
 5. An imagesignal recording and reproducing apparatus for recording an image signalin a recording medium having a plurality of recording tracks, the imagesignal corresponding to successive images screen by screen, comprising:asupplier for continuously supplying image data corresponding to theimage signal, the image data individually representing a plurality ofpixels each responsible for a specific color component; a sound supplierfor continuously supplying an audio signal corresponding to the imagesignal; a processor for generating luminance data for each pixel, basedon the image data,outputting in parallel a pair of separated luminancedata obtained by halving the luminance data generated, generating twotypes of color difference data each corresponding to four pixels, basedon the image data, and outputting a compound color difference dataobtained by alternately combining the two types of color difference datagenerated, by a predetermined unit; a compressing encoder for generatinga pair of compressed luminance data and a compressed color differencedata by giving a compressing operation to the pair of separatedluminance data and the compound color difference data according to apredetermined algorithm; and a modulator for generating a pair ofluminance modulated signals and a color difference modulated signal bygiving an analog modulating operation to the pair of compressedluminance data and the compressed color difference data; a clockcombiner for generating a composite audio signal by superimposing atiming clock signal of a predetermined cycle onto the audio signal; anda recorder for writing the pair of luminance modulated signals, thecolor difference modulated signal, and the composite audio signal ontofirst to fourth parallel recording tracks of the recording medium.
 6. Animage signal recording and reproducing apparatus according to claim 5,wherein:the clock combiner includes a low pass filter having a cut-offfrequency higher than a highest frequency of the audio signal, and lowerthan a frequency of the timing clock signal, and a composite audiosignal is generated by superimposing a timing clock signal onto theaudio signal having passed through the low pass filter.
 7. An imagesignal recording and reproducing apparatus according to claim 5, furthercomprising:a reproducer for reading a pair of luminance modulatedsignals a color difference modulated signal, and a composite audiosignal respectively from the first to fourth recording tracks of therecording medium; a clock separator for individually extracting theaudio signal, and the timing clock signal from the composite audiosignal; a demodulator for generating a pair of compressed luminance dataand compressed color difference data by giving a demodulating operationto the pair of luminance modulated signals and the color differencemodulated signal according to the timing clock signal; and an expandingdecoder for restoring a pair of separated luminance data and compoundcolor difference data by giving an expanding operation according to anidentical algorithm employed by the compressing encoder, to the pair ofcompressed luminance data and the compressed color difference data. 8.An image signal recording and reproducing apparatus according to claim7, wherein:the clock combiner includes a low pass filter having acut-off frequency higher than a highest frequency of the audio signal,and lower than a frequency of the timing clock signal, a composite audiosignal being generated by superimposing a timing clock signal onto theaudio signal having passed through the low pass filter, the clockseparator includes a low pass filter having a cut-off frequency lowerthan a frequency of the timing clock signal and a high pass filterhaving a cut-off frequency higher than a highest frequency of the audiosignal, the audio signal is extracted from the composite audio signal byhaving the composite audio signal to pass through the low pass filter;and the timing clock signal is extracted from the composite audio signalby having the composite audio signal to pass through the high passfilter.
 9. An image signal recording and reproducing apparatus forrecording an image signal in a recording medium having a plurality ofrecording tracks, the image signal corresponding to successive imagesscreen by screen, comprising:a supplier for continuously supplying imagedata indicating values of a plurality of pixels, the pixels beingarranged in a matrix with respect to the image and cyclicallycorresponded to first to third different color components; a signalprocessor for distributing the image signal into a first colorcomponent, a second color component, and a third colorcomponent;generating first separated color component signal and a secondseparated color component signal by halving the first color component,and generating a compound color component signal by combing the firstcolor component and the second color component; and a recorder forwriting the first separated color component signal and the secondseparated color component signal onto a first and second recordingtracks arranged in parallel on the recording medium, and the compoundcolor component signal onto a third recording track on the recordingmedium.
 10. An image signal recording and reproducing apparatusaccording to claim 9, further comprising:a reproducer for reading thefirst separated color component signal, the second separated colorcomponent signal, and the compound color component signal from therecording medium; and a color encoder for generating a luminance signal,a first color difference signal, and a second color difference signalbased on the first separated color component signal, the secondseparated color component signal, and the compound color componentsignal read from the recording medium.
 11. An image signal recording andreproducing apparatus for recording an image signal in a recordingmedium having a plurality of recording tracks, the image signalcorresponding to successive images screen by screen, comprising:a firstsupplier for continuously supplying image data indicating values of aplurality of pixels, the pixels being arranged in a matrix with respectto the image and cyclically corresponded to a plurality of differentcolor components; a signal processor for generating a plurality of colorcomponent signals by dissolving the image signal into each colorcomponent; a second supplier for generating an audio signalcorresponding to the image; a clock combiner for generating a compositeaudio signal by superimposing a clock signal onto the audio signal, theclock signal having a constant cycle in synchronism with the number ofcolor component signals; and a recorder for writing the number of colorcomponent signals and the composite audio signal onto a plurality ofrecording tracks arranged in parallel in the recording medium.
 12. Animage signal recording and reproducing apparatus according to claim 11,further comprising:a reproducer for reading the number of colorcomponent signals and the composite audio signal from the recordingmedium; a color encoder for generating a luminance signal, a first colordifference signal, and a second color difference signal, based on thenumber of color component signals and the composite audio signal readfrom the recording medium; and a clock separator for generating a timingsignal by extracting the clock signal from the composite audio signalread from the recording medium.